This invention relates to low cost high side supply shut down circuits, and, more particularly, to circuits that can deactivate a centralized high side supply. The invention may be used with high side supplied electrical loads, e.g. pressure regulators, solenoid valves, etc. Industrial Applicability includes use in vehicle electro-hydraulic transmission modules to respond in the event of a system-required supply shut down.
In some electronic or electromechanical systems, there are instances in which it is desired to protect an overall system from the adverse impact of an output load driver failure. An output load driver failure or malfunction means, in particular, the inability to control the output load driver. The only way to regain limited control over the system is to deactivate the central load supply, which permits bringing the overall system into a defined and safe mode. The malfunction of an output load driver could have devastating consequences on the overall system with the effect of damaging the downstream load, e.g. hydraulic sub-components, or other equipment. Such driver malfunctions may significantly damage other ancillary equipment (e.g. clutches), or may be dangerous to a human operator of the equipment.
This invention relates to high side supply shut down circuits, and, more particularly, to circuits that can deactivate a centralized high side supply, used with high side supplied electrical loads. Particularly useful examples include, e.g., pressure regulators, solenoid valves, etc., as part of a vehicle electro-hydraulic transmission module in the event of a system requested supply shut down. Such electro-hydraulic transmission modules have and will have everyday use in automobiles, trucks, buses, motorcycles, watercraft, airplanes, spacecrafts, and other engine driven vehicles.
FIG. 1 is a schematic diagram illustrating a prior art example of a solution to activate and deactivate a central supply voltage. Supply voltage 102 is connected between ground and the high side of switch 108. The low side of switch 108 is connected to loads 118, 122, 126. The first load 118 is connected in series to the low side of switch 108. Transistor 116 is connected to the load 118 and to subsequent circuitry or, as indicated, to ground potential. The second load 122 is connected in series with switch 108, as well, and the enabling transistor 120 couples load 122 to ground potential. Similarly, load 126 is connected in series on the low side of switch 108 and is enabled by transistor 124 to ground potential. The high sides of the load circuits 118, 122, and 126 are connected with each other and will be receiving power or no power depending on the operation of switch 108. The enabling inputs 140, 142, 144 to transistors 116, 120, 124 would include any typical input, depending upon the environment in which the circuit is utilized and the required tasks to be undertaken.
Connected to the high side (supply voltage) of the relay switch 108 (also called relay terminals) is relay coil 80 that activates the relay switch 108. The low side of relay coil 80 is connected to transistor 114. In enabled operation, current would flow through relay coil 80 and through transistor 114. The current through the relay coil 80 operates to close switch 108 (or here, the relay terminals 108). With terminals 108 closed, power is supplied to the load circuits 118, 122, and 126. In a predetermined sequence, if a deactivation signal is applied to the input 148 of transistor 114, transistor 114 will be inactivated, thereby interrupting the current flow through relay coil 80. When this current flow is interrupted, terminals 108 open and interrupt the power on loads 118, 122, and 126. The deactivation or activation signal that can be applied to input 148 of transistor 114 is based on a pre-determined strategy or paradigm generated from the diagnostics and control module 160 (e.g. micro-controller or other electronics). If, for example, transistor 116 fails, which could be determined by the diagnostics feedback signal 150 and is not able to deactivate load 118, the diagnostics and control module 160 will send a deactivation signal to the input 148 of transistor 114. Transistor 114 will then interrupt the current flow through relay coil 80. This will interrupt (open) the relay terminals 108 and consequently the power supply for all loads including load 118, which was uncontrollable by transistor 116. The same case example can be exercised regarding transistor 124 with the related feedback signal 152, and transistor 120 with feedback signal 154. In addition to the output driver feedback lines, the system has a feedback 156 for the actual supply voltage to the loads and a feedback 162 measuring the actual voltage 102 on the high side of the relay terminals. The feedback line 158 allows a plausibility check between the status of the relay terminals 108 and the drive status of the relay coil 80. In case of an activated relay coil 80, the low side feedback signal 158 of the relay coil 80 has to be plausible with the high side feedback signal 162 of relay terminals 108 and the low side feedback signal 156 of relay terminals 108 and vice versa.
FIG. 2 is a second prior art supply malfunction load protection strategy similar to that of the prior art solution in FIG. 1. In FIG. 2, a high side semiconductor switch control circuit 86 (also called a field effect transistor, or FET) is substituted for the relay coil 80 and the relay terminals 108 in FIG. 1. Instead of terminals 108, as in FIG. 1, the drain source path of FET 86 is utilized in series with the supply voltage. Instead of relay coil 80, as in FIG. 1, the gate of FET 86 is utilized as control input. In case of a shut down scenario, high side switch control circuit 86 would receive a disabling signal on control line 148. With this disabling signal 148, the power flow to loads 118, 122, 126 would be interrupted. Due to the non-existence of a separate drive circuit (coil 80, as in FIG. 1) and switch circuit (terminals 108, as in FIG. 1), the feedback line 158 of FIG. 1 is not required.
While the circuitry of FIGS. 1 and 2 have been shown in the prior art, these circuits have significant drawbacks. Specifically, in automotive or other vehicle control systems such prior art solutions are based on more expensive semiconductor high side switches or relays that are not feasible for hybrid or surface mounted technology applicable to automotive controllers. High side switches require a charge pump circuit, which makes them cost ineffective and requires space on a hybrid or printed circuit board. Historically, the need for a redundant activation/deactivation path (relay solution, FIG. 1 or high side driver circuit solution, FIG. 2) in automotive controllers was driven by the need to deactivate a faulty low side driver. The goal of such deactivation was to avoid damage to the attached external circuitry, i.e., attempting to limit repair to replacement of the automotive controller. However, that approach is no longer feasible because of upcoming integration of automotive controllers with the formerly external circuitry into non-repairable units. As a result of the circuit integration, the deactivation functionality can be reduced to a one-time malfunction event handling with the entire integrated circuit/controller unit being replaced. Damage to the downstream equipment (e.g. hydraulic sub-components) is no longer critical under these conditions. The goal of this deactivation strategy, in the case of an output driver malfunction, is to avoid devastating situations to other ancillary equipment (e.g. clutches), or danger to a human operator of this equipment.
Accordingly, there is a need in the art for an improved power supply shut down circuit that is suitable for surface mounting, and is cost effective, particularly for integrated controller/circuit units of electro-hydraulic vehicle systems.
The present invention relates to a high side supply shutdown circuit that is surface mountable and is a cost effective solution for integrated controller/circuit units. A principal embodiment includes a fuse that is coupled between the central high side power supply and downstream load circuits. A monitoring circuit for diagnostics purposes is added on the low side of the fuse. Furthermore, the downstream load circuits (e.g. load with low side output driver) have a diagnostic and control link to a diagnostics and control module. This diagnostics and control circuit monitors the downstream load circuit feedback to determine if operations are within parameter specification (plausibility) and controls the operation of the low side output drivers. The diagnostics and control module also controls the shutdown circuit, which deactivates the central power supply by triggering the fuse. In the case of non-plausibility (out of spec condition) of the downstream load circuit feedback, the inventive circuit allows the current through the fuse to exceed the operating level of the fuse when the shutdown transistor receives an enabling signal from the diagnostics and control module. The circuit also includes one or more load circuits coupled to the low side of the fuse, with the load circuits receiving operating current through the fuse.
Further embodiments are also disclosed, including a fuse diagnostic system and method for shutting down the power through the load circuits when a low side output driver or fuse, is in a non-plausible (out of spec) state.